Most wireless devices feature a customized antenna, i.e., an antenna that is designed and manufactured ad-hoc for each device model. This is because each wireless device or, more specifically, each mobile device features a different radioelectric specification and a different internal architecture. Additionally, one of the main requirements demanded of antenna technology developed for wireless devices is to feature reduced dimensions since the available space for the antenna system in such devices is quite small. Consequently, one of the constrains of some antenna technologies when they have to be applied to wireless devices is their size, since the relationship between antenna size and its operating wavelength results in large sizes when small frequency bands need to be covered, such as LTE700, GSM850 or GSM900 in the case of mobile communications. In order to fulfill size requirements, antenna technology has evolved to provide complex antenna architectures that efficiently occupy and make use of the maximum space available inside the device, especially if this is a mobile device, a smartphone and the like.
Since the need for covering more applications is an increasing demand of wireless devices, other requirements related to such devices are large bandwidths and high efficiencies in order to provide good wireless communications. The challenge then is to develop antenna technologies that provide large bandwidths with good antenna efficiencies and that feature reduced sizes to fit in the small available spaces that wireless devices dedicate to the antenna system. One finds in the prior art some solutions proposed to fulfill the mentioned requirements. FIG. 1 shows a prior-art example (WO 2010/015365 A2) that illustrates a solution that provides multiband operation covering two different frequency regions. This solution comprises one structural branch that normally includes a strip line 1 and a radiation booster 2 connected to an end of the strip branch. This single-branch antenna structure protrudes from a ground plane layer 3 that comprises a ground clearance 4 that allocates the antenna structure. Normally, a single-branch solution like the one in FIG. 1 uses a single matching network, such as the one provided in FIG. 3, to match the input impedance of the device and to provide bandwidth at the different frequency bands and/or regions of operation. FIG. 2 displays the bandwidth (1) and the efficiency (2) computed for the example shown in FIG. 1. These curves are obtained by using a typical Electromagnetic CAD tool (e.g., IE3D). Curve (1) shows a two-region bandwidth covering the frequency ranges that go from 824 MHz to 960 MHz and from 1,710 MHz to 2,690 MHz. Curve (2) provides the antenna efficiency related to the mentioned example. The limitations of a single-branch solution emerge when one wants to improve the electromagnetic performance of the device, particularly at low frequency ranges.
Other prior-art solutions comprise an antenna system that includes more than one single-branch structure and a feeding system for each structure, or branch in these cases. Other solutions found in the prior art operate by coupling between branches of their single-branch structures. More details of those solutions are found in WO 2014/012796 A1 and US 2016/0111790 A1, respectively. In general, the solutions that include more than one single-branch structure provide better bandwidths than single-branch solutions but one of their drawbacks is that they feature radiofrequency systems more complex in architecture and in the number of ports. One also may find multi-branch solutions with simpler radiofrequency systems but those can not reach so large bandwidths as the aforementioned solutions and a device related to the system described herein.